Through further development of diodes and transistors in the form of semiconductor electronic and electric circuits have been solidified to be so-called Integrated Circuits (ICs). ICs are mainly made from silicon because of easy handling, rich resource and other good reasons. ICs have met the applicant's highest expectations for solidification of circuits, reduction of manpower, miniaturization, less trouble, economy by mass production and the like, and they are currently widely used in electronic and electric circuits, memories for computers, microcomputers and other components. In the manufacturing processes of such semiconductor devices as above, there is a technology called "photolithography". In photolithography, after having coated about 1 .mu. m thin film of a photoresist, which will become an etching resist, on a silicon wafer which has a silicon oxide film of several 1,000 A, the film is exposed to ultraviolet rays through a mask and images are developed and etched. After having stripped off the photoresist, the wafer is completely cleaned, and dopants are diffused and implated from the exposed area of silicon. By repeating this photolithography several times and, furthermore, by preparing electrodes and wiring, ICs are manufactured. The working geometry or size of photolithography of diodes, transistors and early ICs produced rough figures as 100- scores of .mu.m. Since then, after the superiority of solidified devices had been recognized, a further miniaturization has been made by adding the same functions and/or new functions, efforts were made for increasing the economical aspects, and development has been made for new demands. For this reason, together with the improvement and increase of mask performance, photoresist performance, quality of silicon wafers, performance of mask alignment equipments, diffusion techniques, performance of related chemicals, etching techniques and the like, it has become possible to work for the geometries of 10-4 .mu.m with necessary working accuracy and resulted in the form of Large Scale Integrated Circuit (LSI).
As LSI continuously shows expected performance and economy as a solid device the development of Ultra LSI (commonly expressed as Very Large Scale Integrated Circuits) has recently become very active by making the working geometry of the lithography such that much finer patterns of more limited results of 3-1 .mu.m or below 1 .mu.m with necessary working accuracy can be produced.
In conventional photolithography, because ultra violet rays having wavelengths of from 3,500 to 4,500 A are used they produce diffraction of light and other undesired phenomena, and it has been concluded that it would be impossible to form fine patterns of below 1 .mu.m even if modification or improvements are made or with full utilization of high performance of conventional photolithography. Particularly in the case of mass production, the present invention can provide economical advantages and increase demand and it meets the subject purpose or object, but the extention of conventional techniques cannot provide mass production fine patterns of 1 .mu.m.
In order to obtain resolution of below 1 .mu.m by avoidance of light diffraction to solve the above problem, development is under progress for the application of various energy sources such as electron beam which has a much shorter wavelength than light (approximately 0.5 A) and soft X rays (about 10 A). To explain this development in detail, application of electron beams require large scale equipment which must be operated and used by large scale computers resulting in an extremely expensive system, and in addition to these disadvantages, although there are many available electron beam resists there is no acceptable one, it requires longer exposure times, and there is no practicality in the transfer of images onto the wafers. Furthermore, there is no practical light source (energy source) for application of soft X rays. It has a number of disadvantages such as mask-making is troublesome, mask-adjusting is difficult, there is a physiological dislike, extremely expensive equipment is anticiptated and others. For these reasons, a working technique for an economical mass production of 1 .mu.m or below 1 .mu.m geometry using energy of shorter wavelengths is still considerably difficult to be developed.
In order to solve such existing problems, through utilization of ultra violet rays having a shorter wavelength of from 1,000 to 3,500 A than from 3,500 to 4,500 A as used in the conventional photolithography, and a special photoresist such as Polymethyl Methacrylate (PMMA), it has been discovered that, by reduction of diffraction phenomenon, it is possible to obtain ultra high resolution and a highly accurate resist pattern of 1 .mu.m down to below 1 .mu.m.
However, although ultra fine patterns could be obtained with a single position exposure instead of using a scanning exposure, PMMA was in a disadvantageous position because of its considerably low sensitivity, lack of etching resistance, especially lack of resistance against plasma dry etching, therefore, it could not be used in practical applications.
Because of these reasons, if a photoresist having equivalent to or higher ultra resolution, sensitivity and etching resistance than PMMA against the light source with wavelengths of 1,000-3,500 A, could be found, such a photoresist can be used in the technology of extended conventional photolithography and, in addition to such advantage, because low pressure mercury lamps, deutrium lamps, xenon-mercury lamps and the like, can be used as light sources and it becomes possible to solve the problems with the most economical formation of ultra finer patterns and its practicality.
With such background as mentioned above, the inventors of the present invention, as the result of their research and development, have invented a method to form extremely superior ultra fine patterns without having any one of the above-mentioned defects.